Semiconductor device and manufacturing method thereof

ABSTRACT

A method includes forming a crown structure over a substrate; forming fins in the crown structure; forming an intra-device isolation region between the fins and forming inter-device isolation regions on opposing sides of the crown structure; forming a gate structure over the fins; forming a dielectric layer that extends continuously over the inter-device isolation regions, the fins and the intra-device isolation region; performing an etching process to reduce a thickness of the dielectric layer, where after the etching process, upper surfaces of the inter-device isolation regions and upper surfaces of the fins are exposed while an upper surface of the intra-device isolation region is covered by a remaining portion of the dielectric layer; and forming an epitaxial structure over the exposed upper surfaces of the fins, where after the epitaxial structure is formed, there is a void between the epitaxial structure and the intra-device isolation region.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.15/883,179, filed on Jan. 30, 2018 and entitled “Semiconductor Deviceand Manufacturing Method Thereof,” which is a continuation of U.S.patent application Ser. No. 14/854,915, filed on Sep. 15, 2015 andentitled “Semiconductor Device and Manufacturing Method Thereof,” nowU.S. Pat. No. 9,905,641 issued on Feb. 27, 2018, which applications areincorporated herein by reference.

BACKGROUND

Semiconductor devices are used in a large number of electronic devices,such as computers, cell phones, and others. Semiconductor devicesinclude integrated circuits that are formed on semiconductor wafers bydepositing many types of thin films of material over the semiconductorwafers, and patterning the thin films of material to form the integratedcircuits. Integrated circuits include field-effect transistors (FETs)such as metal oxide semiconductor (MOS) transistors.

In the race to improve transistor performance as well as reduce the sizeof transistors, transistors have been developed that the channel andsource/drain regions are located in a fin formed from the bulksubstrate. Such non-planar devices are multiple-gate FinFETs. Amultiple-gate FinFET may have a gate electrode that straddles across afin-like silicon body to form a channel region.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A to 1F are perspective views of a method for manufacturing asemiconductor device at various stages in accordance with someembodiments of the present disclosure.

FIG. 2 is a cross-sectional view taking along line 2-2 of FIG. 1F.

FIG. 3 is a cross-sectional view of a semiconductor device in accordancewith some embodiments of the present disclosure.

FIG. 4 is a cross-sectional view of a semiconductor device in accordancewith some embodiments of the present disclosure.

FIG. 5 is a cross-sectional view of a semiconductor device in accordancewith some embodiments of the present disclosure.

FIGS. 6A to 6C are cross-sectional views of a method for manufacturing asemiconductor device at various stages in accordance with someembodiments of the present disclosure.

FIG. 7 is a cross-sectional view of a semiconductor device in accordancewith some embodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

FIGS. 1A to 1F are perspective views of a method for manufacturing asemiconductor device at various stages in accordance with someembodiments of the present disclosure. Reference is made to FIG. 1A. Asubstrate 110 is provided. In some embodiments, the substrate 110 may bea semiconductor material and may include known structures including agraded layer or a buried oxide, for example. In some embodiments, thesubstrate 110 includes bulk silicon that may be undoped or doped (e.g.,p-type, n-type, or a combination thereof). Other materials that aresuitable for semiconductor device formation may be used. Othermaterials, such as germanium, quartz, sapphire, and glass couldalternatively be used for the substrate 110. Alternatively, thesubstrate 110 may be an active layer of a semiconductor-on-insulator(SOI) substrate or a multi-layered structure such as a silicon-germaniumlayer formed on a bulk silicon layer.

At least two trenches 112′ are formed in the substrate 110. The trenches112′ may be formed using a masking layer (not shown) along with asuitable etching process. For example, the masking layer may be ahardmask including silicon nitride formed through a process such aschemical vapor deposition (CVD), although other materials, such asoxides, oxynitrides, silicon carbide, combinations of these, or thelike, and other processes, such as plasma enhanced CVD (PECVD), lowpressure CVD (LPCVD), or even silicon oxide formation followed bynitridation, may alternatively be utilized. Once formed, the maskinglayer may be patterned through a suitable photolithographic process toexpose those portions of the substrate 110 that will be removed to formthe trenches 112′.

As one of skill in the art will recognize, however, the processes andmaterials described above to form the masking layer are not the onlymethod that may be used to protect portions of the substrate 110 whileexposing other portions of the substrate 110 for the formation of thetrenches 112′. Other suitable process, such as a patterned and developedphotoresist, may alternatively be utilized to expose portions of thesubstrate 110 to be removed to form the trenches 112′. All such methodsare fully intended to be included in the scope of the presentdisclosure.

Once a masking layer has been formed and patterned, the trenches 112′are formed in the substrate 110. The exposed substrate 110 may beremoved through a suitable process such as reactive ion etching (RIE) inorder to form the trenches 112′ in the substrate 110, although othersuitable processes may alternatively be used. In some embodiments, thetrenches 112′ may be formed to have a depth d1 be less than about 500 nmfrom the surface of the substrate 110, such as about 250 nm. Asexplained below with respect to FIG. 1B, the area of the substrate 110between the trenches 112′ is subsequently patterned to form individualsemiconductor fins.

Reference is made to FIG. 1B. For the sake of clarity, FIG. 1B has beenenlarged from FIG. 1A to show the interior of the trenches 112′ of FIG.1A. At least one trench 114 is formed between the trenches 112′ of FIG.1A, and the trenches 112′ are formed to be trenches 112. For example, inFIG. 1B, two of the trenches 114 are formed between the trenches 112.The trenches 114 can be isolation regions between separate semiconductorfins 116 that share either a similar gate or similar sources or drains.The trenches 112 may be isolation regions located between semiconductorfins that do not share a similar gate, source, or drain.

The trenches 114 may be formed using a similar process as the trenches112′ (discussed above with respect to FIG. 1A) such as a suitablemasking or photolithography process followed by an etching process.Additionally, the formation of the trenches 114 is also used to deepenthe trenches 112′ of FIG. 1A, such that the trenches 112 extend into thesubstrate 110 a further distance than the trenches 114. That is, thetrenches 112 are deeper than the trenches 114. This may be done by usinga suitable mask to expose both the trenches 112 as well as those areasof the substrate 110 that will be removed to form the trenches 114. Assuch, the trenches 112 may have a second depth d2 of between about 20 nmand about 700 nm, such as about 320 nm, and the trenches 114 may beformed to have a third depth d3 of between about 10 nm and about 150 nm,such as about 1000 nm. It is noted that although in FIG. 1B the trenches112 and 114 have sharp corners, in some other embodiments, the trenches112 and 114 may have round corners depending on the etching conditions.

However, as one of ordinary skill in the art will recognize, the processdescribed above to form the trenches 112 and 114 is one potentialprocess, and is not meant to be limited with this respect. Rather, othersuitable process through which the trenches 112 and 114 may be formedsuch that the trenches 112 extend into the substrate 110 further thanthe trenches 114 may be utilized. For example, the trenches 112 may beformed in a single etch step and then protected during the formation ofthe trenches 114. Other suitable process, including any number ofmasking and removal processes may alternatively be used.

In addition to forming the trenches 114, the masking and etching processadditionally forms the semiconductor fins 116 from those portions of thesubstrate 110 that remain unremoved. These semiconductor fins 116 may beused, as discussed below, to form the channel region of thesemiconductor device. While FIG. 1B illustrates three semiconductor fins116 formed from the substrate 110, any number of semiconductor fins 116that are greater than one may be utilized such that there are thetrenches 112 and 114. In some embodiments, the semiconductor fins 116may form a separate channel region while still being close enough toshare a common gate (whose formation is discussed below in relation toFIG. 1D).

Reference is made to FIG. 1C. The trenches 112 and 114 are filled with adielectric material (not shown). The dielectric material is recessedwithin the trenches 112 and 114 to respectively form isolationstructures 122 (referred as second isolation structures or inter-deviceisolation structures) and 124 (referred as first isolation structures orintra-device isolation structures). In some embodiments, the isolationstructures 122 extend into the substrate 110 further than the isolationstructures 124. In other words, the isolation structures 122 are deeperthan the isolation structures 124. The isolation structures 122 define acrown structure (or a crown active region) 102 in the substrate 110, andthe isolation structures 124 define a plurality of the semiconductorfins 116 in the crown structure 102. In greater detail, the crownstructure (or the crown active region) 102 includes the semiconductorfins 116, the isolation structure 124, and a continuous semiconductorregion 104. The continuous semiconductor region 104 is underlying thesemiconductor fins 116 and the isolation structure 124. The dielectricmaterial may be an oxide material, a high-density plasma (HDP) oxide, orthe like. The dielectric material may be formed, after an optionalcleaning and lining of the trenches 112 and 114, using either a CVDmethod (e.g., the high aspect ratio process (HARP) process), a highdensity plasma CVD method, or other suitable method of formation as isknown in the art.

The trenches 112 and 114 may be filled by overfilling the trenches 112and 114 and the substrate 110 with the dielectric material and thenremoving the excess material outside of the trenches 112 and 114 andsubstrate 110 through a suitable process such as chemical mechanicalpolishing (CMP), an etch, a combination of these, or the like. In someembodiments, the removal process removes any dielectric material that islocated over the substrate 110 as well, so that the removal of thedielectric material will expose the surface of the substrate 110 tofurther processing operations.

Once the trenches 112 and 114 have been filled with the dielectricmaterial, the dielectric material may then be recessed away from thesurface of the substrate 110. The recessing may be performed to exposeat least a portion of the sidewalls of the semiconductor fins 116adjacent to the top surface of the substrate 110. The dielectricmaterial may be recessed using a wet etch by dipping the top surface ofthe substrate 110 into an etchant such as HF, although other etchants,such as H₂, and other methods, such as a reactive ion etch, a dry etchwith etchants such as NH₃/NF₃, chemical oxide removal, or dry chemicalclean may alternatively be used. The dielectric material may be recessedto a fourth depth d4 from the surface of the substrate 110 of betweenabout 5 nm and about 50 nm, such as about 40 nm. Additionally, therecessing may also remove any leftover dielectric material located overthe substrate 110 to ensure that the substrate 110 is exposed forfurther processing.

As one of ordinary skill in the art will recognize, however, the stepsdescribed above may be only part of the overall process flow used tofill and recess the dielectric material. For example, lining steps,cleaning steps, annealing steps, gap filling steps, combinations ofthese, and the like may also be utilized to form and fill the trenches112 and 114 with the dielectric material. All of the potential processsteps are fully intended to be included within the scope of the presentembodiment.

Reference is made to FIG. 1D. A gate stack 130 is formed on a portion ofthe semiconductor fins 116 and the isolation structures 122 and 124. Thegate stack 130 includes a gate dielectric 132 and a gate electrode 134.The gate dielectric 132 may be formed by thermal oxidation, chemicalvapor deposition, sputtering, or any other methods known and used in theart for forming a gate dielectric. Depending on the technique of gatedielectric formation, a thickness of the gate dielectric 132 on the topof the semiconductor fins 116 may be different from a thickness of thegate dielectric 132 on the sidewall of the semiconductor fins 116.

The gate dielectric 132 may includes a material such as silicon dioxideor silicon oxynitride with a thickness ranging from about 3 angstroms toabout 100 angstroms, such as about 10 angstroms. The gate dielectric 132may alternatively be formed from a high permittivity (high-k) material(e.g., with a relative permittivity greater than about 5) such aslanthanum oxide (La₂O₃), aluminum oxide (Al₂O₃), hafnium oxide (HfO₂),hafnium oxynitride (HfON), or zirconium oxide (ZrO₂), or combinationsthereof, with an equivalent oxide thickness of about 0.5 angstroms toabout 100 angstroms, such as about 10 angstroms or less. Additionally,combinations of silicon dioxide, silicon oxynitirde, and/or high-kmaterials may also be used for the gate dielectric 132.

The gate electrode 134 is formed on the gate dielectric 132. The gateelectrode 134 may include a conductive material and may be selected froma group including of polycrystalline-silicon (poly-Si), poly-crystallinesilicon-germanium (poly-SiGe), metallic nitrides, metallic silicides,metallic oxides, metals, combinations of these, and the like. Examplesof metallic nitrides include tungsten nitride, molybdenum nitride,titanium nitride, and tantalum nitride, or their combinations. Examplesof metallic silicide include tungsten silicide, titanium silicide,cobalt silicide, nickel silicide, platinum silicide, erbium silicide, ortheir combinations. Examples of metallic oxides include ruthenium oxide,indium tin oxide, or their combinations. Examples of metal includetungsten, titanium, aluminum, copper, molybdenum, nickel, platinum, etc.

The gate electrode 134 may be deposited by chemical vapor deposition(CVD), sputter deposition, or other techniques known and used in the artfor depositing conductive materials. The thickness of the gate electrode134 may be in the range of about 200 angstroms to about 4,000 angstroms.Ions may or may not be introduced into the gate electrode 134 at thisprocess. Ions may be introduced, for example, by ion implantationtechniques.

The gate stack 130 defines multiple channel regions (i.e., firstportions 117) located in the semiconductor fins 116 underneath the gatedielectric 132. The gate stack 130 may be formed by depositing andpatterning a gate mask (not shown) on a gate electrode layer using, forexample, deposition and photolithography techniques known in the art.The gate mask may incorporate commonly used masking materials, such as(but not limited to) photoresist material, silicon oxide, siliconoxynitride, and/or silicon nitride. A dry etching process may be used toform the patterned gate stack 130.

Once gate stack 130 is patterned, a pair of spacers 140 may be formed.The spacers 140 may be formed on opposing sides of the gate stack 130.The spacers 130 are typically formed by blanket depositing a spacerlayer (not shown) on the previously formed structure. The spacer layermay include SiN, oxynitride, SiC, SiON, oxide, and the like and may beformed by methods utilized to form such a layer, such as chemical vapordeposition (CVD), plasma enhanced CVD, sputter, and other methods knownin the art. The spacer layer may include a different material withdifferent or the similar etch characteristics than the dielectricmaterial of isolation structures 122 and 124. The spacers 140 may thenbe patterned, such as by one or more etches to remove the spacer layerfrom the horizontal surfaces of the structure.

In FIG. 1D, at least one of the semiconductor fins 116 has at least onefirst portion 117 and at least one second portion 118. The gate stack130 and the spacers 140 cover the first portion 117 while leaving thesecond portion(s) 118 uncovered. That is, the second portion(s) 118 isexposed by the gate stack 130 and the spacers 140. Moreover, at leastone of the isolation structures 124 has at least one first portion 125and at least one second portion 126. The gate stack 130 and the spacers140 cover the first portion 125 while leaving the second portion(s) 126uncovered. That is, the second portion(s) 126 is exposed by the gatestack 130 and the spacers 140.

Reference is made to FIG. 1E. Parts of the second portions 118 of thesemiconductor fins 116 are removed from those areas not protected by thegate stack 130 and spacers 140. Top surfaces 118 t of the remainingsecond portions 118 of the semiconductor fins 116 are below the topsurfaces 126 t of the second portions 126 of the isolation structure124. This removal may be performed by a reactive ion etch (RIE) usingthe gate stacks 130 and first spacers 140 as hardmasks, or by any othersuitable removal process. In some embodiments, the etching process maybe performed under a pressure of about 1 mTorr to 1000 mTorr, a power ofabout 50 W to 1000 W, a bias voltage of about 20 V to 500 V, at atemperature of about 40° C. to 60° C., using a HBr and/or Cl₂ as etchgases. Also, in the embodiments provided, the bias voltage used in theetching process may be tuned to allow good control of an etchingdirection to achieve desired profiles for the remaining (or recessed)second portions 118 of the semiconductor fins 116. It is noted thatalthough in FIG. 1E the remaining second portions 118 have sharpcorners, in some other embodiments, the remaining second portions 118may have round corners depending on the etching conditions.

Reference is made to FIGS. 1F and 2, and FIG. 2 is a cross-sectionalview taking along line 2-2 of FIG. 1F. An epitaxy structure 160 isformed on the remaining second portions 118 of the semiconductor fins116 and above the second portions 126 of the isolation structures 124,leaving at least one void V on the second portions 126 of the isolationstructures 124. For example, in FIGS. 1F and 2, the epitaxy structure160 leaves two voids V respectively on the second portions 126 of theisolation structures 124. Since the lattice constant of the epitaxystructure 160 is different from the substrate 110, the channel regionsof the semiconductor fins 116 are strained or stressed to enable carriermobility of the device and enhance the device performance. In someembodiments, the epitaxy structure 160, such as silicon carbon (SiC), isepi-grown by a LPCVD process to form source and drain regions of ann-type FinFET. The LPCVD process is performed at a temperature of about400° C. to 800° C. and under a pressure of about 1 to 200 Torr, usingSi₃H₈ and SiH₃CH as reaction gases. In some embodiments, the epitaxystructure 160, such as silicon germanium (SiGe), is epi-grown by a LPCVDprocess to form source and drain regions of a p-type FinFET. The LPCVDprocess is performed at a temperature of about 400° C. to 800° C. andunder a pressure of about 1 to 200 Torr, using SiH₄ and GeH₄ as reactiongases.

The epitaxy structure 160 has a top surface 162. At least one portion ofthe top surface 162 of the epitaxy structure 160 is recessed. That is,the top surface 162 of the epitaxy structure 160 has at least onerecessed surface portion 162 r. Moreover, the top surface 162 furtherhas at least one peak portion 162 p. The recessed surface portion 162 ris local minimum of the top surface 162, and the peak portion 162 p is alocal maximum of the top surface 162. For example, in FIGS. 1F and 2,the top surface 162 has two of the recessed surface portions 162 r andthree of the peak portions 162 p. The recessed surface portions 162 rare respectively located above the second portions 126 of the isolationstructures 124 to respectively form grooves G in the epitaxy structure160. Therefore, the top surface 162 is a wavy surface.

In FIGS. 1F and 2, the epitaxy structure 160 has a bottom surface 164adjacent to the voids V. At least one portion of the bottom surface 164of the epitaxy structure 160 is recessed to form the void V. In FIGS. 1Fand 2, the bottom surface 164 of the epitaxy structure 160 is recessedto form the two voids V. Therefore, the bottom surface 164 is a wavysurface. The voids V is disposed on the second portions 126 of theisolation structures 124, separating the epitaxy structure 160 and thesecond portions 126. The second portions 126 of the isolation structures124 are respectively disposed between the epitaxy structure 160 and thesubstrate 110. In some embodiments, the voids V are air voids (or airgaps), whose permittivity is about 1. The permittivity differencebetween the epitaxy structure 160 and the voids V can achieve goodalternate current (AC) performance.

In some embodiments, at least one of the second portions 118 of thesemiconductor fins 116 has a thickness T1 in a range of about 5 nm toabout 13 nm. At least one of the second portions 126 of the isolationstructures 124 has a thickness T2 in a range of about 5 nm to about 20nm. At least one of the voids V has a thickness T3 greater than about 4nm. A pitch P of adjacent two of the semiconductor fins 116 (i.e.,substantially equals to a pitch of adjacent two of the peak portions 162p) is substantially smaller than 40 nm. A height difference H betweenthe first portion 117 and the second portion 118 of the semiconductorfin 116 is in a range of about 30 nm to about 55 nm.

In some embodiments, after the process of FIG. 1F, a contact (not shown)can be formed on the epitaxy structure 160 to interconnect the epitaxystructure 160 and overlaying structures of the semiconductor device. Insome embodiments, the contact is made of metal, and the claim is notlimited in this respect. In FIGS. 1F and 2, since the epitaxy structure160 has the recessed (wavy) top surface 162, the contact area of thecontact and the epitaxy structure 160 can be increased, thereby reducingthe junction contact resistance, and improve the performance of thesemiconductor device. Moreover, since at least one of the secondportions 118 of the semiconductor fins 116 is disposed between theisolation structures 122 and 124, and the second portions 118, theisolation structures 122 and 124 together form a recess, the (lateral)regrowth of the epitaxy structure 160 can be constrained in the recess.Thus, the growth dislocation problem of the epitaxy structure 160 can beimproved. Furthermore, due to the isolation structures 124, the currentleakage problem of the semiconductor fins 116 and the epitaxy structure160 can be improved. In addition, the permittivity difference betweenthe epitaxy structure 160 and the voids V can achieve good alternatecurrent (AC) performance.

FIG. 3 is a cross-sectional view of a semiconductor device in accordancewith some embodiments of the present disclosure. The difference betweenthe semiconductor devices of FIGS. 3 and 2 pertains to the shapes of theepitaxy structure 160. In FIG. 3, the epitaxy structure 160 includes aplurality of epitaxy portions 166 spaced from each other andrespectively disposed on the semiconductor fins 116. For example, inFIG. 3, the epitaxy structure 160 includes three epitaxy portions 166.The epitaxy portions 166 are facet shaped. In greater detail, due todifferent growth rates on different surface planes, facets may be formedon the epitaxy portions 166. For example, the growth rate on surfaceshaving (111) surface orientations (referred to as (111) planes) is lowerthan that on other planes, such as (110) and (100) planes. Accordingly,facets 167 are formed as a result of the difference in the growth ratesof different planes. If the epitaxy portions 166 are grown freely, thefacets 167 will have the (111) surface orientations (in other word, on(111) planes). Therefore, with the proceeding of the epitaxial growth,due to the difference in growth rates, facets 167 are gradually formed.

In FIG. 3, a void V is formed between adjacent two of the epitaxyportions 166 and on the second portions 126 of the isolation structure124. The void V can be an air void. The permittivity difference betweenthe epitaxy structure 160 and the voids V can achieve good alternatecurrent (AC) performance. Moreover, the shape difference between theepitaxy structure 160 of FIGS. 3 and 2 depends on, for example, theepitaxial growth conditions, and the claimed scope is not limited inthis respect. Other relevant structural details of the semiconductordevice in FIG. 3 are similar to the semiconductor device in FIG. 2, and,therefore, a description in this regard will not be repeatedhereinafter.

FIG. 4 is a cross-sectional view of a semiconductor device in accordancewith some embodiments of the present disclosure. The difference betweenthe semiconductor devices of FIGS. 4 and 2 pertains to the number of thesemiconductor fins 116 and the shape of the epitaxy structure 160. InFIG. 4, the substrate 110 has two semiconductor fins 116, and theisolation structure 124 is disposed therebetween. The top surface 162 ofthe epitaxy structure 160 has one recessed surface portion 162 r and twopeak portions 162 p. The recessed surface portion 162 r is formedbetween the two peak portions 162 p. The recessed surface portion 162 ris located above the second portions 126 of the isolation structures 124to form a groove G in the epitaxy structure 160. Therefore, the topsurface 162 is a wavy surface. Moreover, a void V is formed on thesecond portion 126 of the isolation structure 124 and between theepitaxy structure 160 and the second portion 126. The semiconductordevices having two semiconductor fins 116 can be applied to an n-typemetal-oxide-semiconductor (MOS) device, while the semiconductor deviceshaving three semiconductor fins 116 as shown in FIGS. 2 and 3 can beapplied to a p-type MOS device, and the claimed scope is not limited inthis respect. Other relevant structural details of the semiconductordevice in FIG. 4 are similar to the semiconductor device in FIG. 2, and,therefore, a description in this regard will not be repeatedhereinafter.

FIG. 5 is a cross-sectional view of a semiconductor device in accordancewith some embodiments of the present disclosure. The difference betweenthe semiconductor devices of FIGS. 5 and 3 pertains to the number of thesemiconductor fins 116. In FIG. 5, the substrate 110 has twosemiconductor fins 116, and the isolation structure 124 is disposedtherebetween. The epitaxy structure 160 includes two epitaxy portions166 spaced from each other and respectively disposed on the twosemiconductor fins 116. The epitaxy portions 166 are facet shaped. InFIG. 5, facets 167 are formed as a result of the difference in thegrowth rates of different planes. If the epitaxy portions 166 are grownfreely, the facets 167 will have the (111) surface orientations (inother word, on (111) planes). Therefore, with the proceeding of theepitaxial growth, due to the difference in growth rates, facets 167 aregradually formed. Furthermore, a void V is formed between the twoepitaxy portions 166 and on the second portions 126 of the isolationstructure 124 to improve the AC performance of the semiconductor device.The semiconductor device in FIG. 5 can be applied to an nMOS device, andthe claimed scope is not limited in this respect. Other relevantstructural details of the semiconductor device in FIG. 5 are similar tothe semiconductor device in FIG. 3, and, therefore, a description inthis regard will not be repeated hereinafter.

FIGS. 6A to 6C are cross-sectional views of a method for manufacturing asemiconductor device at various stages in accordance with someembodiments of the present disclosure. The cross-sectional positions ofFIGS. 6A to 6C are similar to the cross-sectional position of FIG. 1F.The manufacturing processes of FIGS. 1A-1D are performed in advance.Since the relevant manufacturing details are similar to theabovementioned embodiment, and, therefore, a description in this regardwill not be repeated hereinafter. Reference is made to FIG. 6A.Subsequently, a sidewall layer 170 is formed along the semiconductorfins 116. The sidewall layer 170 may include a dielectric material suchas silicon oxide. Alternatively, the sidewall layer 170 may includesilicon nitride, SiC, SiON, or combinations thereof. In someembodiments, the sidewall layer 170 can be formed with the spacers 140(see FIG. 1D), or formed in an additional process, and the claimed scopeis not limited in this respect.

Reference is made to FIG. 6B. Parts of the second portions 118 of thesemiconductor fins 116 are removed from those areas not protected by thegate stack 130 and spacers 140. Also, parts of the sidewall layer 170are removed to form a plurality of sidewall structures 175 on the secondportions 126 of the isolation structures 124. Top surfaces 118 t of theremaining second portions 118 of the semiconductor fins 116 are belowthe top surfaces 126 t of the second portions 126 of the isolationstructure 124. This removal may be performed by a reactive ion etch(RIE) using the gate stacks 130 and first spacers 140 (see FIG. 1D) ashardmasks, or by any other suitable removal process. In someembodiments, the etching process may be performed under a pressure ofabout 1 mTorr to 1000 mTorr, a power of about 50 W to 1000 W, a biasvoltage of about 20 V to 500 V, at a temperature of about 40° C. to 60°C., using a HBr and/or Cl₂ as etch gases. Also, in the embodimentsprovided, the bias voltage used in the etching process may be tuned toallow good control of an etching direction to achieve desired profilesfor the remaining (or recessed) second portions 118 of the semiconductorfins 116. It is noted that although in FIG. 6B the remaining secondportions 118 have sharp corners, in some other embodiments, theremaining second portions 118 may have round corners depending on theetching conditions.

In FIG. 6B, during the etching process, since the ions or etchants foretching is not easy to enter the gaps between the semiconductor fins116, the etching thickness of the sidewall layer 170 (see FIG. 6A)between the semiconductor fins 116 are less than other portions.Therefore, in some embodiments, portions of the sidewall layer 170 onthe isolation structures 122 can be removed while the sidewallstructures 175 remain on the isolation structures 124. However, in someother embodiments, portions of the sidewall layer 170 may remain on theisolation structures 122 and have a thickness smaller than the sidewallstructures 175. In some embodiments, the thickness of the sidewallstructures 175 can be greater than 3 nm.

Reference is made to FIG. 6C. An epitaxy structure 160 is formed on theremaining second portions 118 of the semiconductor fins 116 and abovethe second portions 126 of the isolation structures 126, leaving atleast one void V on the second portions 126 of the isolation structures124. For example, in FIG. 6C, the epitaxy structure 160 leaves two voidsV respectively on the second portions 126 of the isolation structures124. Since the lattice constant of the epitaxy structure 160 isdifferent from the substrate 110, the channel regions of thesemiconductor fins 116 are strained or stressed to enable carriermobility of the device and enhance the device performance. In someembodiments, the epitaxy structure 160, such as silicon carbon (SiC), isepi-grown by a LPCVD process to form source and drain regions of ann-type FinFET. The LPCVD process is performed at a temperature of about400° C. to 800° C. and under a pressure of about 1 to 200 Torr, usingSi₃H₈ and SiH₃CH as reaction gases. In some embodiments, the epitaxystructure 160, such as silicon germanium (SiGe), is epi-grown by a LPCVDprocess to form source and drain regions of a p-type FinFET. The LPCVDprocess is performed at a temperature of about 400° C. to 800° C. andunder a pressure of about 1 to 200 Torr, using SiH₄ and GeH₄ as reactiongases.

In FIG. 6C, the epitaxy structure 160 includes a plurality of epitaxyportions 166 spaced from each other and respectively disposed on thesemiconductor fins 116. For example, in FIG. 6C, the epitaxy structure160 includes three epitaxy portions 166. The sidewall structures 175 arerespectively disposed between the epitaxy portions 166 to adjust theprofile of the epitaxy portions 166. The epitaxy portions 166 are facetshaped. In greater detail, due to different growth rates on differentsurface planes, facets may be formed on the epitaxy portions 166. Forexample, the growth rate on surfaces having (111) surface orientations(referred to as (111) planes) is lower than that on other planes, suchas (110) and (100) planes. Accordingly, facets 167 are formed as aresult of the difference in the growth rates of different planes. If theepitaxy portions 166 are grown freely, the facets 167 will have the(111) surface orientations (in other word, on (111) planes). Therefore,with the proceeding of the epitaxial growth, due to the difference ingrowth rates, facets 167 are gradually formed. Moreover, a void V isformed between adjacent two of the epitaxy portions 166 and on thesecond portions 126 of the isolation structure 124 to improve ACperformance of the semiconductor device. Other relevant structuraldetails of the semiconductor device in FIG. 6C are similar to thesemiconductor device in FIG. 2, and, therefore, a description in thisregard will not be repeated hereinafter.

FIG. 7 is a cross-sectional view of a semiconductor device in accordancewith some embodiments of the present disclosure. The difference betweenthe semiconductor devices of FIGS. 7 and 6C pertains to the number ofthe semiconductor fins 116. In FIG. 7, the substrate 110 has twosemiconductor fins 116, and the isolation structure 124 and the sidewallstructure 175 are disposed therebetween. The epitaxy structure 160includes two epitaxy portions 166 spaced from each other andrespectively disposed on the two semiconductor fins 116. The epitaxyportions 166 are facet shaped. Furthermore, a void V is formed betweenthe two epitaxy portions 166 and on the second portions 126 of theisolation structure 124 to improve the AC performance of thesemiconductor device. The semiconductor device in FIG. 7 can be appliedto an n-type MOS device, and the claimed scope is not limited in thisrespect. Other relevant structural details of the semiconductor devicein FIG. 7 are similar to the semiconductor device in FIG. 6C, and,therefore, a description in this regard will not be repeatedhereinafter.

According to the aforementioned embodiments, since the epitaxy structurehas the recessed (wavy) top surface, the contact area of a contact andthe epitaxy structure can be increased, thereby reducing the junctioncontact resistance, and improve the performance of the semiconductordevice. Moreover, since at least one of the second portions of thesemiconductor fins is disposed between the isolation structures, and thesecond portions and the isolation structures together form a recess, the(lateral) regrowth of the epitaxy structure can be constrained in therecess. Thus, the growth dislocation problem of the epitaxy structurecan be improved. Furthermore, due to the isolation structures disposedbetween the semiconductor fins, the current leakage problem of thesemiconductor fins and the epitaxy structure can be improved. Inaddition, the permittivity difference between the epitaxy structure andthe voids can achieve good alternate current (AC) performance.

According to some embodiments, a semiconductor device includes asubstrate, at least one first isolation structure, at least two secondisolation structure, and an epitaxy structure. The substrate has aplurality of semiconductor fins therein. The first isolation structureis disposed between the semiconductor fins. The semiconductor fins aredisposed between the second isolation structures, and the secondisolation structures extend into the substrate further than the firstisolation structure. The epitaxy structure is disposed on thesemiconductor fins. At least one void is present between the firstisolation structure and the epitaxy structure.

According to some embodiments, a semiconductor device includes aplurality of inter-device isolation structures, at least one crownactive region, and an epitaxy structure. The crown active region isdisposed between the inter-device isolation structures, and the crownactive region includes a plurality of semiconductor fins, at least oneintra-device isolation structure, and a continuous semiconductor region.The intra-device isolation structure is disposed between thesemiconductor fins. The continuous semiconductor region is underlyingthe semiconductor fins and the intra-device isolation structure. Theepitaxy structure is disposed on the semiconductor fins. At least oneair gap is present between the intra-device isolation structure and theepitaxy structure.

According to some embodiments, a method for manufacturing asemiconductor device includes forming at least one first isolationstructure and a plurality of second isolation structures in a substrate.The second isolation structures define a crown structure in thesubstrate, and the first isolation structure defines a plurality ofsemiconductor fins in the crown structure. A gate stack is formedoverlaying first portions of the semiconductor fins and a first portionof the first isolation structure while leaving second portions of thesemiconductor fins and a second portion of the first isolation structureexposed. Parts of the second portions of the semiconductor fins areremoved. An epitaxy structure is formed on the remaining second portionsof the semiconductor fins. The epitaxy structure leaves a void on thesecond portion of the first isolation structure.

In an embodiment, a semiconductor device includes a plurality ofinter-device isolation structures; and a crown active region disposedbetween the plurality of inter-device isolation structures, where thecrown active region includes a first semiconductor fin and a secondsemiconductor fin immediately adjacent to the first semiconductor fin;an intra-device isolation structure disposed between the firstsemiconductor fin and the second semiconductor fin; an epitaxy structureincluding a first portion on the first semiconductor fin and a secondportion on the second semiconductor fin, where a bottommost surface ofthe epitaxial structure is below a top surface of the intra-deviceisolation structure, where an air gap is between the intra-deviceisolation structure and the epitaxy structure; and a dielectric layer onthe intra-device isolation structure, the dielectric layer extendingcontinuously along the top surface of the intra-device isolationstructure from a first sidewall of the first portion of the epitaxystructure to a second sidewall of the second portion of the epitaxystructure facing the first sidewall.

In an embodiment, a method for manufacturing a semiconductor deviceincludes forming a first isolation structure and a plurality of secondisolation structures in a substrate, where the plurality of secondisolation structures define a crown structure in the substrate, and thefirst isolation structure defines a plurality of semiconductor fins inthe crown structure; forming a gate stack over the plurality ofsemiconductor fins; forming a dielectric layer over upper surfaces ofthe plurality of second isolation structures, over an upper surface ofthe first isolation structure, and over upper surfaces of the pluralityof semiconductor fins; performing an etching process, where the etchingprocess removes portions of the dielectric layer to expose the uppersurfaces of the plurality of second isolation structures and the uppersurfaces of the plurality of semiconductor fins, where after the etchingprocess, a remaining portion of the dielectric layer covers an entireupper surface of the first isolation structure; and forming an epitaxystructure on the plurality of semiconductor fins, where the epitaxystructure leaves at least one void over the first isolation structure.

In an embodiment, a method for manufacturing a semiconductor deviceincludes forming a crown structure over a substrate; formingsemiconductor fins in the crown structure; forming an intra-deviceisolation region between the semiconductor fins and forming inter-deviceisolation regions on opposing sides of the crown structure; forming agate structure over the semiconductor fins; forming a dielectric layerthat extends continuously over the inter-device isolation regions, thesemiconductor fins and the intra-device isolation region; performing anetching process to reduce a thickness of the dielectric layer, whereafter the etching process, upper surfaces of the inter-device isolationregions and upper surfaces of the semiconductor fins are exposed whilean upper surface of the intra-device isolation region is covered by aremaining portion of the dielectric layer; and forming an epitaxialstructure over the exposed upper surfaces of the semiconductor fins,where after the epitaxial structure is formed, there is a void betweenthe epitaxial structure and the intra-device isolation region.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor device comprising: a substrate;inter-device isolation structures over the substrate; and a crown activeregion between the inter-device isolation structures, wherein the crownactive region comprises: a first semiconductor fin and a secondsemiconductor fin adjacent to the first semiconductor fin; anintra-device isolation structure between the first semiconductor fin andthe second semiconductor fin; a source/drain structure comprising afirst portion on the first semiconductor fin and comprising a secondportion on the second semiconductor fin, wherein an air gap is betweenthe intra-device isolation structure and the source/drain structure; anda dielectric layer on the intra-device isolation structure, thedielectric layer physically contacting and extending continuously alongan upper surface of the intra-device isolation structure from the firstportion of the source/drain structure to the second portion of thesource/drain structure, wherein upper surfaces of the inter-deviceisolation structures distal from the substrate and proximate to thecrown active region are free of the dielectric layer.
 2. Thesemiconductor device of claim 1, wherein a first thickness of theintra-device isolation structure is smaller than a second thickness ofthe inter-device isolation structures.
 3. The semiconductor device ofclaim 1, wherein the first semiconductor fin and the secondsemiconductor fin are recessed below an upper surface of theintra-device isolation structure.
 4. The semiconductor device of claim1, wherein the first portion of the source/drain structure and thesecond portion of the source/drain structure merge to form a continuoussource/drain region.
 5. The semiconductor device of claim 4, wherein anupper surface of the continuous source/drain region facing away from thefirst semiconductor fin has at least one groove.
 6. The semiconductordevice of claim 1, wherein the first portion of the source/drainstructure is spaced apart from the second portion of the source/drainstructure.
 7. The semiconductor device of claim 1, further comprising agate structure over the first semiconductor fin and the secondsemiconductor fin.
 8. The semiconductor device of claim 1, wherein athickness of the dielectric layer is greater than about 3 nm.
 9. Asemiconductor device comprising: a substrate; a crown structureprotruding above the substrate, the crown structure comprising: aplurality of fins; an intra-device isolation structure between theplurality of fins; source/drain regions over the plurality of fins; anda dielectric layer over and in physical contact with the intra-deviceisolation structure, wherein the dielectric layer is between theplurality of fins; and an inter-device isolation structure over thesubstrate and on opposing sides of the crow structure, wherein an uppersurface of the inter-device isolation structure distal from thesubstrate is free of the dielectric layer.
 10. The semiconductor deviceof claim 9, wherein the source/drain regions comprise a first portiondirectly over a first fin of the plurality of fins, and comprise asecond portion directly over a second fin of the plurality of fins. 11.The semiconductor device of claim 10, wherein the dielectric layerextends continuously along an upper surface of the intra-deviceisolation structure from a first sidewall of the first portion of thesource/drain regions to an opposing second sidewall of the secondportion of the source/drain regions.
 12. The semiconductor device ofclaim 10, wherein the source/drain regions extend continuously from thefirst fin to the second fin.
 13. The semiconductor device of claim 10,wherein the first portion of the source/drain regions has a first peak,and the second portion of the source/drain regions has a second peak,wherein a pitch between the first peak and the second peak issubstantially equal to a pitch between the first fin and the second fin.14. The semiconductor device of claim 9, wherein a lower surface of theintra-device isolation structure facing the substrate extends furtherfrom the substrate than a lower surface of the inter-device isolationstructure facing the substrate.
 15. The semiconductor device of claim14, wherein an upper surface of a first fin of the plurality of finsdistal from the substrate is closer to the substrate than an uppersurface of the intra-device isolation structure distal from thesubstrate.
 16. A method for manufacturing a semiconductor device, themethod comprising: forming inter-device isolation structures over asubstrate; forming a crown structure between the inter-device isolationstructures, the crown structure comprising semiconductor fins and anintra-device isolation structure between the semiconductor fins; forminga gate structure over the semiconductor fins; forming a dielectric layerover the crown structure and over the inter-device isolation structures,wherein the dielectric layer is formed to be in physical contact withthe intra-device isolation structure and the inter-device isolationstructures; and recessing the semiconductor fins using an etchingprocess, wherein the etching process removes the dielectric layer fromthe semiconductor fins and from the inter-device isolation structures,wherein after the etching process, the dielectric layer over theintra-device isolation structure remains, and upper surfaces of theinter-device isolation structures distal from the substrate are free ofthe dielectric layer.
 17. The method of claim 16, wherein recessing thesemiconductor fins recesses upper surfaces of the semiconductor finsbelow an upper surface of the intra-device isolation structure.
 18. Themethod of claim 16, further comprising, after recessing thesemiconductor fins, forming source/drain regions on the semiconductorfins.
 19. The method of claim 18, wherein the source/drain regionsextend continuously over the semiconductor fins, wherein there is a voidbetween the source/drain regions and the dielectric layer disposed overthe intra-device isolation structure.
 20. The method of claim 16,wherein the etching process is a plasma etching process.